The targeting vector was designed with a loxP::frt-SV40 promoter-Neo-pA-frt cassette 389 bp upstream of exon 12, and a loxP site 676 bp downstream of exon 12. Cre-mediated recombination removed exon 12. Western blot analysis of heart and brain tissues confirmed that no protein was expressed in mutant mice. (J:231609)